SITE INFORMATION AND CORRESPONDENCE 1980-1999

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changes to less than 0.5 is without appropriate technical basis and should be removed from the Permit. The Basin Plan specifies that "[C]hanges in the normal ambient pH levels shall not exceed 0.5....[I]n determining compliance,...appropriate averaging periods may be applied provided that the beneficial uses will be fully protected" (emphasis added). If the Regional Board does not remove the Delta pH from the proposed Permit, an appropriate averaging period should be given. A twelve-month rolling average is recommended as appropriate and will avoid classifying the discharge as in non-compliance when no beneficial use impacts are apparent. 4. General Comments on Nuisance or Adverse Affect to Beneficial Use The City requests that the Regional Board include in the receiving water limitations, where applicable, the limitation that a violation of receiving water limits is tied to those that "cause nuisance or adversely affect beneficial uses." For example, the Basin Plan provides for such a limitation to tentative receiving water F 3, 4, 5 (e.g., "water shall be free of discoloration that causes nuisance or adversely affects beneficial uses.") See, Basin Plan at III-5.00. BOD The City requests the effluent BOD to be changed to Carbonaceous BOD (Permit, B1). EPA recommends the use of CBOD when establishing water quality-based limits to avoid test interference. EPA allows the use of BOD or CBOD in setting technology- based limits. As the proposed limits are water quality-based, the City requests CBOD limits be included in the permit. Furthermore, there is no data in the record to support the imposition of year- round stringent BOD limits. As such, the City requests seasonal limits from the prior permit be maintained because oxygen demand typically is a problem, during May through C. October. NPDESPermitComments Exhibit 2 Page 23 12/17/99